1. Field of the Invention
The present invention relates to electric contacts which perform an electrical opening and closing operation in an electric circuit, an electric contact apparatus, and a method for detecting abrasion of the electric contacts.
2. Description of the Related Art
In each of electric devices for a high voltage such as a circuit breaker, a disconnector and a switching device in a power station or a substation, electric contacts for opening and closing an electric circuit are provided.
In view of cost and the environment adaptation, the electric devices tend to be made more compact, and also the electric contacts tend to be made smaller.
On the other hand, as electric power demand increases, a power voltage and electric capacity of the electric devices increases. As a result, the current densities of the electric contacts made smaller increase.
In each of the electric devices, a breaking operation is repeated under a high voltage. Thus, part of the electric contacts is evaporated or abraded by an arc heat generated at the time of opening and closing of the electric contacts. In order to correctly operate the electric contacts, and improve the operating rate of each electric device, it is important to accurately gauge the limit of abrasion of the electric contacts.
Examples of the conventional apparatus or method for detecting abrasion of electric contacts are disclosed in Jpn. Pat. Appln. KOKAI Publications No. 6-14501, No. 10-241481 and No. 11-354341, which will be hereinafter referred as literatures 1, 2 and 3, respectively.
Literature 1 discloses a method in which a magnet is attached to a brush, and its magnetic change is detected.
Literatures 2 and 3 respectively disclose a technique in which a piezoelectric element is attached to electric contacts, and its voltage change is monitored, and a technique in which a vibration sensor or an acceleration sensor is attached to a switching device, and an abnormal vibration of a main body, etc. are detected.
In all literatures 1–3, a sensor or the like is provided close to the electric contacts, and variation of electrical or mechanical characteristics of the electric contacts is measured, and it is detected whether an abnormality has occurred or not, based on the result of measurement.
In the conventional apparatus or method for detecting abrasion of electric contacts, variation of the characteristics of the electric contacts which is caused by deformation or abrasion thereof is measured to indirectly detect whether an abnormality has occurred or not.
Accordingly, in the conventional apparatus or method, an abnormality of the electric contacts is detected after it occurs, i.e., it is not detected before it occurs. That is, although the conventional apparatus or method detects an abnormality at an early stage, it cannot detect an abnormality before it occurs. Furthermore, when abrasion of the electric contacts is detected by the conventional apparatus or method, it is necessary to detect indirect variation of the characteristics. Thus, there is a case where the number of malfunctioning of, e.g., a sensor, such as a disturbance of a magnetic field, is increased.
Accordingly, before occurrence of an abnormality, the conventional apparatus or method can hardly directly detect that abrasion of the electric contacts has reached the limit of abrasion.